This invention relates to a method for agglomerating and sintering iron and zinc ore and ore concentrates, steel mill ferrous waste and zinc mill waste. It also relates to sinter bed compositions comprising agglomerated particles of steel mill ferrous wastes or zinc mill wastes.
A variety of iron or zinc rich by-products is produced in steel or zinc mills respectively. These by-products, generally referred to as mill wastes, principally comprise mill scale, various dusts, including ore fines, furnace dusts, open hearth dusts, basic oxygen dusts, open hearth dusts blast furnace flue dusts, spark box fines and grit chamber dusts, and sludges produced at various points in the mills. These by-products may contain a substantial amount of iron or zinc, as the case may be, and the balance is composed of various other materials such as carbon, lime, slag, silica, etc. The large particles of mill waste can be screened out and returned to the blast furnace, but the finer particles must be agglomerated before they are reused.
The major way of agglomerating the mill wastes before reuse is known as sintering. The sintering process is essentially the recycling center for the mill, allowing the by-product materials to be used to increase the yield of steel and/or zinc. In conventional sintering processes the waste material, generally intimately mixed with finely divided fuel such as coke or anthracite, is agglomerated by tumbling it in a drum while it is sprayed with water. The wet agglomerated material is then fed to the traveling grate of a sintering machine where it is formed into a uniform homogeneous bed known as the sinter bed. Near the head or feed end of the grate, the bed is ignited on the surface, and as the mixture moves along on the traveling grate, air is pulled down through the mixture to burn the fuel by downdraft combustion. As the grate moves towards the discharge end, the combustion front in the bed moves progressively downward. This creates sufficient heat and temperature, about 1300xc2x0 C. to about 1500xc2x0 C., to sinter the fine particles together into porous clinkers.
In this process, high permeability of the sinter bed is important in order to obtain rapid and uniform sintering. The height of the sinter bed, and consequently the amount of material that can be sintered in a given time, is limited by fines which can develop when the agglomeration water evaporates, and which blind the permeability of the sinter bed.
There is a need in the industry for agglomeration agents which will minimize the amount of fines and thus allow higher sinter bed heights to be utilized.
According to the present invention there is provided a method for agglomerating and sintering iron and zinc ore and ore concentrates, steel mill ferrous waste and zinc mill waste, comprising: a) mixing the wastes or ore with a combustion fuel source, and a sinter agglomeration agent selected from the group consisting of sodium silicate, water soluble polymers and aqueous emulsions of oils to form an agglomerated sinterable mixture comprising agglomerated particles; b) forming the sinterable mixture into a sinter bed on the grate of a sinter machine; and c) igniting the sinter bed to create a temperature sufficient to sinter the agglomerated particles.
In another embodiment of the invention there is provided a sinter bed composition comprising agglomerated particles of steel mill ferrous wastes or zinc mill wastes comprising a sinter agglomeration agent selected from the group consisting of sodium silicate, water soluble polymers and oil.